Air-speed control system



. 29, 1953 H. s. HENDRlcKsoN AIR SPEED CONTROL SYSTEM Filed Jan. 2l,1950 Patented Dec. 29, 1953 Ara- SPEED CONTROL SysrEM-L Harold S;Hendrickson, Hempstead, N: Yj., asvsignor to The Sperry CorporationGreat Neck Nf-Y.,4 a corporatongof Delaware't Applicationlanuary 21,1950; SerialNo. 139,943?

8; Claims.

This invention relates to: improvementsfin the art; of automatic controlofaircraft, andparticularly toairspeed control. Airspeed'depend's upon;among other things, the amount of: powersup- Dliedf by the propulsionsys-tern; and it can be varied within limits-by adiustn'ient` offfuel`ilow control means such as a throttle or. throttles; Copending U. S.patent'application. now Pate-nt 2,626,757, dated January 27, 1953, ofRichard N.

Bromley, and entitled Automatic Speed- Control` System; describes and,claims asystem whereinv the throttle offan aircraftmotor isoperatedautoumaticallyY according to'Y small deviations; in the airspeedtfroin a'.selected value to I keep the craft iiying substantially at.' saidAselect'edairspeed;

Since therairspeed-does not depend solely.- upon throttlevopeninggzthe'throttle is notrsetwith respect` toia Xed-ireterencefposition inresponse to` airspeed deviation, but' is' set'with respect to aitemporary reference position; whichV is eiiect the position. it Was-injust' before the airspeeddeviation. or error was detected and? utilizedto reset the throttle; This' arrangement permits a repeat back loop forniatchingthe displacement ofthe; driven'v device. (the-throttle) againstthe input control signal (airspeed error) vsimilar to that usedin moreconventional.controler servo-v motor` systems,- and'Y minimizes or'eliminates steady-state .errors-.which otherwise would he -produced"hysuch. factors asv the loadingand'attit'udel of the craftiandrtheadjustment ci naps andpr'o'* heller pitch;

While the above described?` Bromley systemis entirely satisiactoryincasesvtvhere only the airspeed and vfactors not directlyrelatedthereto(for example, direction of flight) are` under control, it has. beenround that cyclic variation iii-speed or hunting` Willuresultif anattempt is'made touse this system in combination' with automaticapproach systems which control the elevator surfaces to make the craftfollow a1 selected glide path. This difficulty results from the factthat the airspeed depends upon the pitch attitude of the craft, but achange inpitch attitude is fol-flowed" by; ratherl than' simultaneouslyaccompanied by; a change in airspeed;

Thus, if the-craft is above the' glide path,` the elevators will becontrolled to make the craftily' 2'V decrease" the speedf still further,calling for an undulyr large increase in throttleopening. Theoscillations in speed may die down after twoor threecycles,v ormaycontinue as long as theautomaticapproachv system Works. to maintainthe:v

craft on the glidepath. Iny either event-,. such oscillations are:highly undesirable,.and they will be re-excited each time the glide`path control system calls fora correction, either in the down- Warddirection as just described, or inthe upf- Ward-direction.`

Oneof the principal-objects ofthe present inf-v ventionis-to providemethods and. meansforprea venting: orminimizing huntingdn Iautomaticairspeed control systems;

More'spe-ciiically,` it is an objectV of this invention to controlairspeed n ot only as aV functionof; airspeed deviation,` loutj alsoasa' functionH of deviation position of the aircraft vertically: withrespect to ak predetermined flight path'or glide path, which;` ofcourse, is closely associated with., and normally correctedfonhy achangeI in attitudeof the craft to causer ascentor descent-to a new orcorrected flight. path.

In another aspect, one of theobjects is to pro-f vide.improvedautomaticapproach or glide pathsysternsi-nwhich the.- airspeedf,as wellv as theerally an airspeed'met'er comprising avcha'mber 3vcontainingv a Sylphon bellows 5. Total air pressure, il e. static plusvelocity head issuppliedto the interior ofthe bellows' 5i through a tube1,

which connected' outsidethe aircraft to a Pit'otvr tube,.not shown.Another tube' @supplies staticv air. pressure to the' chamber 3 outside'the bel-4 lovvsi.V A rod. Ivv isl'rsecored't'o the bellowstoj'be moved.thereby as the bellows'expands andconj`v tractsV vvith varia'ti'onsf'inairspced.. The',v lojngi tuc'lin'alposi'tio'n'ofth'ev rod 'l is ameasure? offairspeed, which may be indicated" by'a dial and' pointerarrangement" I 3'cou'ple'd vtothe' rod I. I` by a racl'candpinion l5;

A signal pickoi device- |71' is'providedin thev chamber 3 andisarrangedto 'be coupled tothe rod,L Il. The device'v Il* includes" anE'shaped coren #9i-of magnetic material, and-*an armature v2pc-'garni2|. A winding 23 on the central leg of the core |9 is connected to analternating current source 25. Pickup windings 21 and 29 on the outerlegs of the core I9 are connected in series opposition so that when thearmature 2| is in its central position, equal and opposite voltages areinduced in the coils 21 and 29 and the net output is zero. When thearmature 2| is displaced one way, say to the left, more voltage isinduced in the coil 21 than in the coil 29, and the difference, which isthe net output, is a function of the displacement and is in phase withthe voltage of the source 25. When the armature 2| is displaced theother way, the output voltage is likewise a function of thedisplacement, but is 180 degrees out of phase with the source 25.

The armature 2| is normally biased to its central position by means ofsprings 3|. It may be engaged with the rod I I by means of a magneticclutch device 33 which as illustrated herein comprises a U-shaped yoke35 secured to the armature 2| and provided with holes 31 through whichthe rod passes loosely. The yoke carries a solenoid magnet 39 whosearmature 4I has a hole 43. The rod also passes loosely through the hole43. The solenoid 39 is connected through a switch 45 to a direct currentsource 41. switch 45 is closed, the solenoid 39 pulls its armature 4|up, gripping the rod I I between the lower side of the hole 43 and theupper sides of the holes 31, and thus couples the armature 2| to the rodI When the switch 45 is open, the rod I is free to move independently ofthe armature 2|, which is then maintained at its central position by thesprings 3 I.

The above described airspeed indicator and pickoff is substantially thesame as that described in the previously mentioned Bromley patent, andis utilized as explained hereinafter to provide a control signalcorresponding to the deviation in airspeed from the selected value. Inaccordance with the present invention, a further signal, correspondingto vertical deviation of the craft from a selected night path, iscombined with the airspeed-deviation signal to control the airspeed.

To produce the vertical deviation signal a radio glide path system maybe used. This includes a ground transmitter 51 which producesoverlapping differently modulated field pattern lobes or otherdirectionally characteristic radiation dening a particular flight path.The aircraft carries a receiver 59 responsive to the transmitter 51 andcontaining the necessary detector apparatus to provide an output signalcorresponding to vertical deviation of the craft above or below theflight path. Such radio glide path -apparatus is well known andtherefore is not described in detail here.

The receiver means 59 may be arranged to provide a direct voltage outputwhose magnitude depends upon the extent of the vertical deviation, andwhose polarity depends upon whether the craft is above or below thedesired flight path. This output is supplied to a conventional crosspointer indicator 6| to control the position of the nominally horizontalpointer 83, and to the pitch or elevator control input terminals of anautomatic pilot mechanism, not shown.

The vertical deviation signal from the receiver 59 is also applied to amodulator 65, which is connected to the A.C. supply 25 to provide anA.C. output which varies in amplitude and phase according to themagnitude and polarity of the signal from the receiver 59. The outputcircuit of When the `displacement of the armature 2| the modulator 65 isconnected in series with the windings on the airspeed pickoff l1, andthe combined airspeed and vertical deviation signals are applied to theinput terminals 5| of a phase detector 49. The connections are such thatthe vertical deviation signal corresponding to deviation above the glidepath is of the same phase as the airspeed pickoff signal correspondingto toward the core leg carrying the coil 29, i. e. to the right in thedrawing. An adjustable voltage divider 61 is provided in the outputcircuit of the modulator 65 for regulating the effect of the verticaldeviation signal upon the composite control signal.

The phase detector 49, which is of known type and may be identical withthat described in the -aforementioned Bromley patent, has referencephase input terminals 53, and output terminals 55. The reference phaseinput terminals are connected to the A.C. source 25. of the detector 49is a direct voltage whose magnitude depends upon the amplitude of theA.C. input to the terminals 5|, and whose polarity depends upon whethersaid A.-C. input is in phase or 180 degrees out of phase with the source25.

The output of the phase detector 49 is applied to a voltage dividercomprising two series-connected resistors 69 and 1|. The voltageappearing across the resistor 69 goes through a rate circuit ordifferentiating circuit 13, which may be a high-pass filter, for examplean L-section RC circuit. The voltage across the resistor 1| is added bya series connection to the output terminals of the rate circuit 13,providing a cornbined voltage which is proportional to the sum of theoutput of the phase detector 49 and the time derivative of said output.

A balanced amplifier 15, which may comprise two substantially identicalD.C. amplifiers, includes two sets of input terminals 11 and 19 andcorresponding pairs of output terminals 8| and 83. The two amplifiersections may be made to have equal gains, so that equal voltages at theinput terminals 11 and 19 will produce equal output voltages at theterminals 8| and 83.

A reversible motor is provided with two field windings 81 and 89 whichare connected to the output terminals 8| and 83 respectively of theamplifier 15. The armature of the motor 85 is connected to the D.C.source 41 by Way of the switch 45. The shaft of the motor 85 is coupledto a tachometer generator 9|, which may be a small permanent magnetD.-C. generator.

I'he generator 9| is connected to a voltage divider comprising seriesconnected resistors 93 and 95. Any voltage across the resistor 93 goesto an integrating circuit 91, which may be simply a low-pass filter. Theoutput terminals of the integrating circuit are connected in series withthe resistor 95 to the input terminals 19 of the balanced amplifier 15.The connections are so arranged that the output of the generator 9|,after passing through the amplifier 15, is applied to the field 89 ofthe motor 85 in such polarity as to oppose the rotation of the motor 85and generator 9|.

The shaft of the motor 85 is also coupled through reduction gearing 99to a throttle operating mechanism I0| or other mechanism by which theengine of the craft is controlled. This mechanism includes a flangedtubular member |03 loosely supporting one or more rings |05 providedwith manually operable throttle control handles |01 and connected torespective throttles as by. cables |09. The rings |05 vare separatedfrom The output' each. other and from the flange on the member |03 byfriction washers I I I.

A solenoid magnet I I3 is connected tothe D..C. source 41 through theswitch 45, and its plunger carries a shaft H5 which extends. through thetubular member It and supports a disc. II'I coaxially at the end of thering and Washer assembly. When the switch 45 isV closed, the solenoidIIS forces the disc il] to the left, compressing the rings IE5 andwashers IiI together and` against theange on the member It?, thuscoupling" the motor 8.5. to thev throttles.

In the. operation of the. described system, the switch 45 is initiallyleft open and the thrcttles (assumingthat. the. craft has more than one.en-1 gine). are adjusted manually to. equalize the loads on the enginesand to. bring the craft to the desired airspeed, as indicatedr by thedial and pointer I3.- The craft is also maneuvered to. place it on thedesired glide path, as indicated bythe meter 6I. During this time thepickof armature Il remains centered, the motor is deenergized, and thethrottle operating mechanism is` disengaged.

When the desired airspeed is attained, the switch is closed, energizingthe solenoids 39 and [i3 to couple the pickoff armature 2l to the rod IIin the airspeed meter and couple the motor 85 to. the throttles, as wellas energizing the armature of the motor 85. As long as the airspeedremains at the selected value, the picko i3' produces no. output.Assuming for the resent that the craft remains on theselected glidepath, there will be no signal applied to the input terminals 'E7 of theamplifier 15. Also, since the motor d and the generator 9| arestationary, no signal will appear at the input terminals 19. Accordinglyneither of the field windings 8'! and 85 will be energized and the motorS5 will continue to re mai-n stationary.

Upon increase or decrease of airspeed, the pickoffl I'I will produce anairspeed errorA signal, corresponding to the airspeed deviation. Thissignal is converted to D.C. by the detector t9, modied by the ratecircuit 13, and amplified by the lower side of the balanced amplifier'i5 to energze the iield 8'! of the motor 35. The polarity of thisenergization depends upon whether the airspeed is above or below theselected value, and the motor rotates accordingly to close or openthethrottles. At the same time, the motor 85. drives the tachometergenerator 9 I. The outputof the generator SI isa signal proportional tothe rate or speed of the throttle motion, and consequently is.;approximately proportional to. the rate of change of airspeed aseifected by the throttle motion.` The integrating circuit provides anoutput which approximates the time integral vof the throttle speedsignal, and is therefore roughly proportional to the accumulated change,in throttle, position. Sincey the integrating circuit 91 will dischargeslowly, either through the input circuit of the amplifier 'I5 or througha resistor pro--` videdv for that purpose, its output is not trulyproportional to the throttle, displacementr and Will gradually decreaseto zero as the throttle rate signal becomes zero. This throttledisplacement signal, in addition to the part of the throttle rate signalappearing across the resistor 95, is amplified by the upper side of thebalanced amplifier to energize the eld 89 of the motor 85, in suchpolarity as to oppose the present rotation. When the. sum of thethrottle displacement and throttle rate signals becomes equal to the sumof the airspeed error and error rate signals, the Iields 31 and 88 areenergized equally and oppositely, and

6. the. motor stops. If the arspeed error has diminished to zero by thistime, all of the signals to the amplifier 'I5 become zero and bothk eldsil?!` and 89 are deenergized. If there is still an airspeed error, or afurther change in airspeed. 0ccurs, the operation will continue orrepeat until the airspeed is adj-usted to the selected value.

The system so far described has special appli cation and advantages foruse in automatic approach systems` for-aircraft Where the craft is ap-`proaching' a landing eld on a radio glide path beam, or in fact,Whenever the craft is following a. radio. path in elevation. In suchcase any deviation above or below the selected path will make the craftnose down or nose up to correct the error. Since it takes less power toily down than to ily level', and more power to fly up, the airspeed willtend to increase or decrease as vertical deviationsr from the glide pathare corrected by the elevator control.

In the present system, these changes in airspeed are anticipated andsubstantially prevented by adding a portion of the vertical deviation oraltitude error signal, to the airspeed error signal.

The modulator 65 converts thereversible-polarity D.C. vertical errorsignal to a reversible phase A.C. signal similar to thel airspeed errorsignal. Since the change in airspeed caused by theelevator control lagsthe vertical deviation from the glide path, the voltagev divider El maybe adjusted to add the airspeed error signal just enough of the altitudeerror signal to compensate forthe change in airspeed.

Now, assuming that the airspeed is at the desired value but the craftgets above or below the desired path, a signal initiated by receiver 59and introduced into voltage divider STI Will first ber applied as anairspeed correction signal to the airspeed control system, including themotor 85 while the altitude is being corrected through that portion ofthe signal from receiver 59 which goes to the elevator control of thegyro pilotv and before the airspeed is changed as the result of a changein the elevator controls. Thus the airspeed will remain substantiallyconstant through* out the automatically controlled vertical maneuveryand the initiation of hunting is prevented. If the airspeed changes fromsome other cause while the altitude is being corrected, the airspeederror signal will further ac-tuate the motor 85,`

in the same manner as if the craft were in levell night, to correct theairspeed.

Since many changes could be made in the above construction and manyapparently widely different embodiments of this invention could be madewithout departure from the scope thereof, it is intended that all mattercontained in the above description or shown in the accompanyingvdrawings shall be interpreted as illustrative and` not in a limitingsense.

What is claimed is:

1. An aircraft speed control system for automatic approach to landingfields inclu-ding means responsive both to airspeed of the craft and todeviation of the aircraft from a selected radio flight path to provide acontrol signal, means responsive to said control signal for moving thelengine throttle so asA to maintain the airspeed of' the craftsubstantially at a selected value, means for producing a rate signalproportional to therate of such throttle movement, means for integratingsaid signal, and means for modifying said control signal by saidintegrated signal to furnish a follow-back throttle dis-placementcorrection which. decays with timeA l 2. An aircraft speed controlsystem for automatic approach to landing elds including airspeedmeasuring means, means responsive thereto to provide a signal dependenton deviation in airspeed of the craft from a selected airspeed value,means for providing a further signal dependent on vertical deviation ofthe aircraft from a selected flight path, means for combining saidsignals in such sense that deviation above the selected flight pathprovides a signal which aids the signal provided in response todeviation above the selected airspeed, means responsive to said combinedsignals to move the engine throttle to prevent changes of airspeed dueto flight path corrections, means for producing a rate signalproportional to the rate of such throttle movement, means forintegrating said signal, and means for modifying said control signal bysaid integrated signal to furnish a follow-back throttle displacementcorrection which decays with time.

3. An aircraft speed control system including airspeed' measuring means,pick-off means responsive thereto to provide a signal dependent ondeviation in airspeed of the craft from a selected airspeed value, meansfor providing a further signal dependent on vertical deviation of theaircraft from a selected flight path, means for combining said signalsin such sense that deviation above the selected ight path provides asignal component which aids the signal component provided in response todeviation above the selected airspeed, servomotor means adapted tocontrol the position of a speed device such as a throttle, means forproviding a displacement signal corresponding initially to adisplacement of said servomotor from an initial position, means forgradually reducing said displacement signal to zero, and means forenergizing said servomotor in accordance with the difference betweensaid combined signals and said displacement signal.

4. An aircraft speed control system including an airspeed meter, anelectrical pick-off and means for coupling said pick-off to said meterto provide a signal voltage dependent on deviation in airspeed of thecraft from a selected airspeed value, a radio glide path system forproviding a further signal voltage dependent on vertical deviation ofthe aircraft from a selected flight path, means for combining saidsignals in such sense that deviation above the selected flight pathprovides a voltage component which aids the voltage component providedin response to deviation above the selected airspeed, servomotor meansadapted to control the position of a speed control device such as athrottle, means for providing a signal voltage corresponding to the rateof displacement of said servomotor, means for integrating said ratesignal voltage to provide a displacement signal, means for energizingsaid servomotor in accordance with the difference between said combinedsignals and said displacement signal, andmeans for gradually reducingsaid displacement signal to Zero.

5.1A control system for aircraft speed control comprising an airspeedmeasuring means, a picko associated therewith for supplying an errorsignal dependent on and proportional -to deviation in airspeed of thecraft from a selected alrspeed value, means for supplying a secondsignal dependent on and proportional to change in the crafts position inelevation, a throttle valve for controlling the airspeed of saidaircraft, a servomotor connected to operate said throttle valve, meansfor supplying a follow-back signal proportional to servomotor speed,means for integrating said last signal to provide a throttledisplacement signal substantially proportional to a time integral ofsaid signal, means for causing said signal to decay with time, wherebyit slowly decreases to zero regardless of the final resting position ofthe throttle, and means for controlling said servomotor in accordancewith the combination of all of said signals.

6. An aircraft speed control system for automatic pilots for automaticapproach to landing elds including a selective airspeed measuringdevice, means for obtaining a signal therefrom proportional to theamount and sign of the error between the selected and measured airspeed,a glide path receiver detecting deviation from the approach glide path,means connected thereto giving a second control signal proportional tothe amount and sign of the deviation, means for obtaining from at leastone of said signals a signal proportional to the time rate of changethereof, an engine throttle servomotor, means for obtaining therefrom asignal proportional to the movement thereof and operative meansconnecting said servomotor to a combination of all the aforesaid signalsto control said throttle servo, whereby throttle readjustment isaccelerated upon either loss of airspeed or departure from the desiredglide path. Y

'7. An aircraft automatic approach system for the automatic pilots ofaircraft having an automatic elevator control, including a radioreceiver of the glide path type, means connected thereto providing acomponent signal proportional to the amount and sign of verticaldeviation of the aircraft from a selected radio glide path, meansoperatively connecting through said signal, said receiver and elevatorcontrol for controlling the pitch attitude of the craft, engine controlmeans, a servomotor for adjusting said means, a selective airspeedresponsive device, means connected thereto providing a further componentsignal proportional to the amount and sign of deviation of the airspeedfrom the selected value, means producing a third component signalproportional to the time rate of change of at least the signal from theairspeed device, and circuit means connecting the three combinedcomponent signals to operate said servomotor.

8. An aircraft automatic approach system including a radio glide pathreceiver providing a signal proportional to the amount and sign ofvertical deviation of the aircraft from a selected glide path, anelevator controller, means operatively connecting said signal to saidcontroller for continuously controlling the pitch attitude of the craft,an airspeed responsive device providing a further signal proportional tothe amount and sign of deviation in airspeed from a selected value, anengine controlling servomotor, means for producing a temporary signalproportional to initial movement of said servomotor, and operative meansfor combining said three signals to control said servomotor.

HAROLD S. HENDRICK-SON.

References Cited in the le of this patent UNITED STATES PATENTSv NumberName Date 2,133,285 Dunmore Oct. 18, 1938 2,191,250 Fischel Feb. 20,1940 2,311,642 Crane et al Feb. 23, 1943 2,464,629 Young Mar. l5, 19492,496,294 Kellogg Feb. '7, 1950 2,496,809 Moseley Feb. '7, 1950

